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Convert Kilojoules to Watt Hours - Energy Converter

This converter translates energy expressed in kilojoules (kJ) into watt‑hours (Wh). The relationship is based on the SI definition of the joule and the derived unit watt‑hour (1 Wh = 3600 J). Use this tool to convert lab results, engineering calculations, battery energy values, or documentation between these commonly used energy units.

The underlying relationship is exact under the SI definitions and widely used in engineering and regulatory contexts. For clarity and traceability we follow national metrology guidance on unit definitions and present concise formulas so you can reproduce the result independently.

If you require high-precision reporting for calibration certificates or regulatory filings, check instrument uncertainty and round conservatively. See the FAQs for guidance on precision, context (energy vs power), and converting related rates such as kJ per hour to watts.

Updated Nov 6, 2025

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Methodology

We use SI-consistent unit definitions: 1 joule (J) is the SI unit of energy. A watt‑hour (Wh) is defined as one watt of power delivered for one hour, and exactly equals 3600 joules.

A kilojoule is 1,000 joules. The conversion from kilojoules to watt‑hours therefore reduces to dividing the energy in joules by 3600. This computation is exact given the SI definitions and is the same approach recommended by national metrology institutes.

When presenting results, consider the required number of significant figures based on measurement uncertainty. For laboratory or instrument readings, use the calibration certificate to select appropriate rounding. Where applicable, cite SI definitions or your lab's traceability chain in reports.

Worked examples

Example 1: 10 kJ → Wh: 10 ÷ 3.6 = 2.777777... Wh (commonly rounded to 2.78 Wh for three significant figures).

Example 2: 0.5 kJ → Wh: 0.5 ÷ 3.6 = 0.138888... Wh (rounded to 0.139 Wh if reporting three significant figures).

Further resources

Expert Q&A

What is the exact numeric relationship between kJ and Wh?

1 kJ = 1000 J and 1 Wh = 3600 J, so 1 kJ = 1000/3600 Wh = 1/3.6 Wh ≈ 0.2777777778 Wh. Use Wh = kJ ÷ 3.6 for direct conversion.

How many significant figures should I report?

Match the number of significant figures to your measurement uncertainty or instrument calibration certificate. If the input is from a device with ±1% uncertainty, reporting two to three significant figures is reasonable; for certification-level values follow the lab's traceability requirements.

Is this conversion different from converting kilojoules per hour to watts?

Yes. Kilojoules (kJ) and watt‑hours (Wh) are energy units. Kilojoules per hour (kJ/h) is a power rate and converts to watts (W). To convert kJ/h to W, use W = (kJ/h × 1000) ÷ 3600 = kJ/h ÷ 3.6.

Can I convert battery capacity reported in kJ to Wh for comparison?

Yes. Convert the battery energy from kJ to Wh using Wh = kJ ÷ 3.6 so you can compare directly with typical battery ratings (which are usually in Wh). Ensure the battery rating and measured energy refer to the same conditions (nominal vs usable capacity).

How does instrument calibration affect this conversion?

The conversion itself is exact, but the accuracy of reported energy depends on measurement instruments and their calibration. Use calibration certificates and uncertainty budgets to determine how to round and whether additional corrections (e.g., sensor drift, environmental factors) are needed.

Where can I find authoritative references for these unit definitions?

National metrology and standards organizations publish SI definitions and unit relationships. The NIST and international SI documents list the definitions used here and are appropriate references for technical reports and regulatory filings.

Sources & citations